Method of manufacturing an electric discharge tube or an electric lamp

ABSTRACT

A method of manufacturing an electric discharge tube or an electric lamp starting from a vessel wherein a closed holder is placed which is provided with a quantity of one or more substances to be introduced into the vessel. Subsequently, a desired gas atmosphere is brought about in the vessel and the vessel is closed. Finally the holder is opened by means of current passage through a heating element present in the vessel. The heating element is connected to the ends of an electric conductor placed in the vessel, for example, a coil, between which ends an electric voltage difference is profuced by means of induction with the aid of a current-conveying primary coil placed outside the vessel.

Unite States Ridders et at.

ateut [191 1 Feb. 26, 1974 U.S. Philips Corporation, New York, N.Y.

[22] Filed: July 12, 1972 [211 App]. No.: 271,058

Related US. Application Data [73] Assignee:

[63] Continuation of Ser. No. 49,379, June 24, 1970,

abandoned.

[30] Foreign Application Priority Data June 27, 1969 Netherlands 6909890 [52] US. Cl. 316/14, 313/177 [51] int. Cl. H0lj 9/38 [58] Field of Search 316/1, 3, 14, 27; 313/177 [56] References Cited UNITED STATES PATENTS 3,230,027 1/1966 Mayer 316/16 3,300,037 l/l967 De Santis 313/177 FOREIGN PATENTS OR APPLICATIONS 1,130,086 5/1962 Germany 313/177 Primary Examiner-Roy Lake Assistant Examiner-J. W, Davie Attorney, Agent, or Firm-Frank R. Trifari [5 7 ABSTRACT A method of manufacturing an electric discharge tube or an electric lamp starting from a vessel wherein a closed holder is placed which is provided with a quantity of one or more substances to be introduced into the vessel. Subsequently, a desired gas atmosphere is brought about in the vessel and the vessel is closed. Finally the holder is opened by means of current passage through a heating element present in the vessel. The heating element is connected to the ends of an electric conductor placed in the vessel, for example, a coil, between which ends an electric voltage difference is profuced by means of induction with the aid of a current-conveying primary coil placed outside the vessel.

2 Claims, 8 Drawing Figures PATENTEB FEBZG I974 Fig.3

@A Mot AGFNT METHOD OF MANUFACTURING AN ELECTRIC DISCHARGE TUBE OR AN ELECTRIC LAMP This is a continuation, of application Ser. No.

49,379, filed June 24, 1970 now abandoned.

The invention relates to a method of manufacturing an electric discharge tube or an electric lamp, starting from a vessel wherein a closed holder is placed which is provided with a quantity of one or more substances to be introduced into the vessel. Furthermore the invention relates to a vessel intended for using such a method and to an electric discharge tube or an electric lamp manufactured in accordance with such a method. The invention particularly relates to a method of manufacturing a low-pressure mercury vapour discharge lamp.

The introduction of a quantity of a substance into a vessel, for example, vacuum discharge tubes, gas discharge tubes and electric lamps, which vessel is closed in its finished state and may contain a given gas filling in addition to the introduced substance, encounters many difficulties in practice, especially'when a very accurate dosage of the substance to be introduced and a very accurate composition of the gas atmosphere are required such as, for example, in low-pressure mercury vapour discharge lamps.

When manufacturing such low-pressure mercury vapour discharge lamps, the mercury required in the lamp is generally introduced with the aid of a dosing device which forms part of a so-called exhaust machine. Completely assembled lamps the interior of which communicates with the ambiance by means of an exhaust tube at one or at both ends of the lamp are applied to this exhaust machine. Different further manufacturing steps are performed on the exhaust machine, such as firing of the lamp envelope and the electrodes, activating the electrodes, vacuum exhaustion, filling with ignition gas and sealing off. Prior to sealing off the mercury-containing dosing device introduces a quantity of mercury through one of the exhaust tubes within the lamp envelope. This known method has many drawbacks. In the first place the mercurycontaining dosing device constitutes a great complication for the exhaust machine. In the second place the mercury is introduced into a vessel which is brought to a high temperature and which is in open communication with the exhaust machine. As a result it is inevitable that a portion of the introduced mercury evaporates and disappears from the lamp, or a portion of the filling gas is driven out of the lamp. Furthermore the introduction of mercury through the exhaust tube involves the risk of mercury getting stuck in the exhaust tube so that after sealing off the lamp it contains too little or no mercury at all. For these reasons a large excess of mercury, namely a multiple of the quantity required in the lamp is generally introduced. Finally, working with mercury on the exhaust machine requires additional safety precautions on medical grounds.

The drawbacks described hereinbefore particularly for low-pressure mercury vapour discharge lamps may be obviated by placing the substance to be introduced into the vessel in a closed holder in the vessel, whereafter the vessel is provided with the desired gas filling and is subsequently closed. The holder is not opened until all manufacturing steps relating to the exhaust process have been completed. Such a method is known, for example, from United Kingdom patent specification No. 926,387 which describes a method of introducing a quantity of mercury into a glow discharge tube. According to the said patent specification the mercury-containing holder is opened by the passage of current through a filament sealed in the holder which filament is connected to a current source with the aid of supply wires passing to the exterior through the wall of the tube. This known method has, however, the great drawback that additional lead-through wires through the wall of the tube are required.

According to the invention, a method of manufacturing an electric discharge tube or an electric lamp, starting from a vessel wherein a closed holder is placed which is provided with a quantity of one or more substances to be introduced into the vessel and wherein subsequently a desired gas atmosphere is brought about whereafter the vessel is closed and wherein finally the holder is opened by the passage of current through a heating element present in the vessel is characterized in that the heating element is connected to the ends of an electric conductor placed in the vessel and that an electric voltage difference is generated between the ends of the conductor by means of induction with the aid of a current-conveying primary coil placed outside the vessel.

In a method according to the invention the transformer principle is used so that it is possible to generate the electric voltage for the heating element within the vessel without the use of current supply wires which are passed through the wall of the vessel. According to the invention it is possible to open the holder at any desired moment during the manufacture of the tube or lamp by placing the primary coil connected to an alternating voltage source around the vessel.

The conductor placed in the vessel may be a secondary coil to which the heating element is connected. In case of suitable choice of the alternating voltage for the primary coil it is possible to use a secondary coil which comprises one turn constituted by a resilient metal strip and the heating element connected to the ends of the strip. The holder is then clamped between the strip and the heating element using the resilience of the strip.

A method according to the invention may be used, for example, for introducing a getter into vacuum discharge tubes or for introducing a certain component of the gas mixture in gas discharge tubes.

A method according to the invention provides special advantages in the manufacture of a low-pressure mercury vapour discharge lamps which comprises a discharge space and two electrodes and wherein the closed holder is made of glass and contains the desired quantity of mercury. According to the invention, one turn whose ends are connected to the heating element and which is placed around one of the electrodes and substantially coaxially with the discharge space is then used as an electric conductor.

When using such a method according to the invention, a discharge vessel is preferably used which in addition to a closed holder containing mercury and a heating element includes an open annular metal strip whose ends are connected to the heating element.

A similar ring is known per se and is present in most low-pressure mercury vapour discharge lamps to prevent blackening of the lamp ends by material sputtered from the electrode during operation of the lamp, and furthermore to decrease the electrode losses which reduce the arc voltage during operation and increase the specific luminous flux of the lamp. For performing a method according to the invention this known ring, which is arranged insulated from the electrode, need only be modified to a slight extent. Notably it is necessary that the ring is not closed but has an interruption so that the ends of the ring thus formed do not establish electrical contact with each other. The location of the ring in the lamp, namely around one electrode near one end of the lamp is very favourable, for itis possible to induce an electric voltage in the ring in a very efficient manner with the aid of a coil arranged around the relevant end of the lamp.

It is alternarively possible to use an open ring of metal wire gauze around tone of the electrodes. Wire gauze cages are known per se and are used to suppress radio interference by low-pressure mercury vapour discharge lamps.

The electric resistance of the ring or the cage and that of the heating element must be chosen to be such that the heating element is brought to a high temperature when the voltage is applied to the primary coil so that the glass holder is melt open. In that case, however, the ring or the cage must remain at a comparatively low temperature so that no unwanted gas can escape from the ring or the cage.

According to the invention a method of manufacturing a low-pressure mercury vapour discharge lamp provides considerable advantages as compared with the known method, wherein a mercury-containing dosing device placed on the exhaust machine is used. According to the invention a much more accurate dosing is possible and much less mercury may be sufficient because the mercury cannot be lost. Furthermore, the mercury introduced into the lamp contains much fewer inpurities. The mercury-containing dosage device on the exhaust machine may be omitted so that this machine becomes simpler and safer. Finally it is of paramount importance that the mercury is released in the lamp only when it is necessary there, namely after sealing off the lamp. As a result it is avoided that the mercury gives rise to unwanted variations in filling pressure during the manufacture of the lamp.

According to the invention a discharge vessel intended for the manufacture of a low-pressure mercury vapour discharge lamp preferably includes a metal strip which is deformed in such a manner that the edges of the ends of the open ring constitute a berth for the mercury-containing holder. The heating element then urges the holder in a clamping manner onto the berth using the resilience of the open ring. In an advantageous embodiment of this discharge vessel at least one of the ends of the ring is provided with a bent edge so that an abutting face is formed for the holder thus preventing the holder from sliding between the ends of the ring and, possibly, from getting loose in the lamp.

The heating element in the above-mentioned discharge vessel preferably consists of a filament, for example, of molybdenum and/or tungsten. It is alternatively possible to use a metal strip, for example, of chrome-iron or chrome-nickel as a heating element.

In a preferred embodiment of a discharge vessel according to the invention wherein the metal strip constitutes a berth for the holder, the glass holder is a mainly cylindrical capsule wherein a wire, preferably a copper-clad wire or a chromium iron wire, is sealed in along the axis. The heating element which urges the capsule onto the berth is provided in such a manner that it intersects the sealed-in wire substantially at right angles. As a result it is avoided that upon opening the capsule glass of this capsule gets loose in the lamp.

In a discharge vessel intended for the manufacture of a low-pressure mercury vapour discharge lamp according to the invention it is alternatively possible to form the heating element as a filament, for example, of molybdenum and/or tungsten a number of turns of which is provided in a clamping manner around the holder. In this embodiment no special berth for the holder is required.

In a further embodiment, which is preferred in some cases, the mercury-containing holder is a mainly cylin drical capsule which is provided on the open ring near one of the ends. The capsule is then secured in a clamping manner with the aid of two strips depressed from the ring and the heating element, which is connected to the ends of the open ring, is secured in such a manner that it remains in mechanical contact with the capsule. The resilience of the open ring may be used for this purpose.

In a discharge vessel intended for the manufacture of a low-pressure mercury vapour discharge lamp the holder may alternatively contain an inert gas in addition to mercury, for example, a quantity of the gas which serves as an ignition gas in the lamp and/or a filler gas. This has the advantage that the mercurycontaining holders can be manufactured in an easier manner and that the holders in the lamp can be opened in an easier manner.

A method or a discharge vessel according to the invention provides special advantages in the manufacture of low-pressure mercury vapour discharge lamps which include a metal which can constitute an amalgam with mercury. In fact, for such lamps an accurate dosing of mercury is very important.

In order that the invention may be readily carried into effect, a few embodiments thereof will now be de scribed in detail by way of example with reference to the accompanying diagrammatic drawing, in which FIG. 1 is an elevational view of an electric conductor, a heating element and a holder for use in a method according to the invention and FIG. 2 is a cross-section of FIG. 1 taken on the plane II II.

FIG. 3 shows one end partially in a cross-section of a discharge vessel for a low-pressure mercury vapour discharge lamp according to the invention and FIG. 4 is a cross-section of the vessel of FIG. 3 taken on the plane IV IV.

FIG. 5 shows an embodiment of a ring, a heating element and a holder for use in a method of manufacturing a low-pressure mercury vapour discharge lamp according to the invention, and

FIG. 6 is a cross-section of the part of tje device of FIG. 5 taken on the plane VI VI between the arrows.

FIG. 7 shows on an enlarged scale an embodiment of a holder which may be used in a method according to the invention and FIG. 8 shows the same holder in its open state,

The device according to FIG. 1 and FIG. 2 includes a resilient metal strip 1 whose ends 4 and 5 are connected by a heating element formed as a filament 2. The filament 2 is tightly stretched along the strip 1. By

bending the strip 1 a closed turn comprising strip 1 and filament 2 is formed and a berth is created for a glass holder 3. The holder 3 is kept in place by the resilience of the strip 1 and includes a quantity of rare gas. The device according to FIGS. 1 and 2 may be used for introducing a component of the gas mixture into gas discharge tubes.

In FIGS. 3 and 4 the reference numeral 6 denotes the wall of a low-pressure mercury vapour discharge lamp the end of which is accommodated in a lamp cap 7 which includes current supply terminals 8. The current supply terminals 8 are connected to the electrode 11 (FIG. 4) of the lamp by means of current supply wires which are passed through the pinch 9. A ring 12 of a 6 mm wide and 0.15 mm thick iron strip is placed around the electrode 11. The ring 12 is secured to the pinch 9 by means of a supporting terminal 13, and is electrically insulated from the electrode 11. The ring 12 is not closed and one of its ends has a bent edge 16 which constitutes an abutting face for a cylindrical glass holder 15. The holder contains mgs of mercury and argon at a pressure of approximately 1 atmosphere. A heating element 14 is tightly stretched across the holder 15 and is secured to the ends of the ring 12. The reference numeral 17 denotes a primary coil provided outside the lamp. When connecting the coil 17 to an alternating voltage source, a voltage different is induced between the ends of the ring 12. A current will then flow through the filament 14 which is connected to the ends of the ring 12 so that the holder 15 melts open. Due to the resilience of the ring 12, the mechanical contact between filament 14 and holder 15 is ensured and the filament 14 will cut deeper and deeper into the holder 15 when it melts open.

FIGS. 5 and 6 show further embodiments of a device for the introduction of mercury into a low-pressure mercury vapour discharge lamp according to the invention. In this case, too, a metal strip ring 18 to be placed around one of the electrodes is used, the ends 19 and 20 of which ring do not establish contact with each other. A glass holder 21, which contains the desired quantity of mercury, is clamped near the end 19 of the ring between two strips 22 and 23 depressed from the ring. A filament 24 is connected to the ends of the ring and as a result of the resilience of the ring it is maintained in mechanical cintact with the holder 21. Upon opening the holder, glass ridges are produced at the area of the recess in the holder so that, if the holder breaks into two halves, these halves are prevented from falling off the ring.

FIGS. 7 and 8 show on an enlarged scale a crosssection ofa holder which may be used in the manufacture of a low-pressure mercury vapour discharge lamp according to FIGS. 3 and 4, and wherein the occurrence of loose glass in the lamp is inhibited in a different manner. The cylindrical holder 25 of lead glass or of chalk glass is approximately 8 mms long and has a wall thickness of approximately 0.2 mms and an external diameter of approximately 2 mms. The holder contains 15 mgs of mercury 26 and argon up to a pressure of approximately 1 atmosphere. A 200 pt thick copper-clad wire 27 is sealed in along the axis of the holder. The Figures also show the heating element 28 of 150 p. thick molybdenum wire. The filament 28 is clamped against the holder 25 and intersects the sealed-in copper-clad wire 27 at substantially right an said discharge space.

gles. FIG. 8 shows the holder in its open state. When the holder breaks into two halves due to cracking upon opening, the copper-clad wire 27 will retain these halves behind the filament 28 so that they cannot get loose in the lamp.

When using the holder according to FIG. 7 in a lamp according to FIG. 3, the heating element was found to have a temperature of approximately l,700 C upon opening while the ring was only brought to a temperature of approximately 200 C at which temperature the ring did not release a noticeable quantity of gas.

What we claim is:

1. In a method for the manufacture of an electric lamp comprising steps of:

filling a meltable-walled holder with pre-selected materials for subsequent release;

closing said holder;

providing a resilient metal strip within the envelope of the lamp, the strip having ends which are spaced apart so as to avoid electrical contact;

employing the resilience of said metal strip to clamp and press the holder against the strip by a filamentary heating element, said heating element being affixed to respective end portions of said strip and electrically contacting said strip to provide a single turn secondary induction element;

introducing a desired atmosphere into said envelope;

closing said envelope;

surrounding the envelope with a primary induction element; and

melting and cutting the walls of the holder to slowly release the preselected materials by applying an alternating voltage to the primary induction element, said voltage causing an induced current in the filamentary heating element for heating said heating element to a sufficient temperature to melt the walls of the holder, the cutting occurring as a result of the tension applied to the heating element by the metal strip, said melting and cutting thereby avoiding glass fragments within the lamp.

2. The method of claim 1 wherein said lamp is a low pressure mercury vapor discharge lamp which includes a discharge space and two electrodes, the closed holder being of glass and containing a desired quantity of mercury and wherein the ends of said single turn are connected to the heating portion and wherein the turn is placed around one of the electrodes and the holder and turn are positioned substantially along the axis of 

1. In a method for the manufacture of an electric lamp comprising steps of: filling a meltable-walled holder with pre-selected materials for subsequent release; closing said holder; providing a resilient metal strip within the envelope of the lamp, the strip having ends which are spaced apart so as to avoid electrical contact; employing the resilience of said metal strip to clamp and press the holder against the strip by a filamentary heating element, said heating element being affixed to respective end portions of said strip and electrically contacting said strip to provide a single turn secondary induction element; introducing a desired atmosphere into said envelope; closing said envelope; surrounding the envelope with a primary induction element; and melting and cutting the walls of the holder to slowly release the preselected materials by applying an Alternating voltage to the primary induction element, said voltage causing an induced current in the filamentary heating element for heating said heating element to a sufficient temperature to melt the walls of the holder, the cutting occurring as a result of the tension applied to the heating element by the metal strip, said melting and cutting thereby avoiding glass fragments within the lamp.
 2. The method of claim 1 wherein said lamp is a low pressure mercury vapor discharge lamp which includes a discharge space and two electrodes, the closed holder being of glass and containing a desired quantity of mercury and wherein the ends of said single turn are connected to the heating portion and wherein the turn is placed around one of the electrodes and the holder and turn are positioned substantially along the axis of said discharge space. 